With increase of network bandwidth, the network transmission rate becomes higher and higher, and people's requirements on voice quality in communication become higher and higher. To meet people's requirements on voice quality, more and more embedded voice codecs are developed. An embedded voice codec is a codec formed by a core layer and several extension layers. The core layer is generally a conventional narrowband or wideband codec, and the extension layers may be wideband, super wideband or even full-band extensions, or may be stereo multi-channel extensions. The embedded voice codec is compatible with a conventional codec, and provides more extension functions as required.
To enable communication between different embedded codecs, transcoding is required, namely, decoding and then coding. The conventional transcoding method generally is: decoding an encoded stream that passes through a first encoder, and then encoding the stream by using a second encoder ready for transcoding. As shown in FIG. 1, at the time of transcoding, a core-layer stream encoded by the first encoder and all received extension-layer streams are decoded, and are then encoded again by the second encoder ready for transcoding. The encoding and decoding method and bandwidth used at part even all of the extension layers before the transcoding are consistent with those after the transcoding.
In the case that the encoding method and the encoding bandwidth for part even all of the extension layers before the transcoding are consistent with those after the transcoding, the use of the transcoding method in the prior art will definitely increase complexity of encoding and decoding and impairs signal quality.